Oscillator having a limiter composed of a symmetric active clamp

Abstract

Disclosed is an oscillator circuit comprised of a sharp bandpass filter having an input and an output; a linear gain stage having an input and an output, the output of the sharp bandpass filter being connected to the input of the linear stage; a limiter having an input and an output, the output of the linear stage being connected to the input of the limiter; and a feedback loop having an input and an output, the output of the limiter being connected to the input of the feedback loop and the output of the feedback loop being connected to the input of the sharp bandpass filter, wherein the improvement being comprised of the limiter being a symmetrical active clamp.

I claim: 
     
       1. An oscillator circuit comprised of a sharp bandpass filter having an input and an output; a linear gain stage having an input and an output, the output of the sharp bandpass filter being connected to the input of the linear stage; a limiter having an input and an output, the output of the linear stage being connected to the input of the limiter; and a feedback loop having an input and an output, the output of the limiter being connected to the input of the feedback loop and the output of the feedback loop being connected to the input of the sharp bandpass filter, wherein the improvement being comprised of: the limiter being comprised of a symmetrical active clamp.   
     
     
       2. An oscillator circuit as recited in claim 1, wherein the limiter has means for clamping a positive input signal producing a clamped positive output signal;   means for clamping a negative input signal producing a clamped negative output signal; and   means for summing the clamped positive output signal of the limiter with the clamped negative output signal of the limiter.   
     
     
       3. An oscillator circuit as recited in claim 2, wherein the symmetrical active clamp is comprised of: a positive polarity clamp comprised of a positive differential amplifier having a negative input terminal connected to receive an input signal Vin, a positive input terminal connected to a positive reference voltage, an output terminal connected to produce said clamped positive output signal, and a feedback loop connecting the output terminal of the positive differential amplifier to the negative input terminal of the positive differential amplifier such that the positive polarity clamp clamps positive polarity input signals;   a negative polarity clamp comprised of a negative differential amplifier having a negative input terminal connected to Vin, a positive input terminal connected to a negative reference voltage, an output terminal connected to produce said clamped negative output signal and a feedback loop connecting the output terminal of the negative differential amplifier to the negative input terminal of the negative differential amplifier such that the negative polarity clamp clamps negative input signals; and   a third amplifier having an input terminal and an output terminal, wherein the input terminal of the third amplifier is connected to both the output terminal of the positive polarity clamp and to the output terminal of the negative polarity clamp such that the output of the positive polarity clamp and the output of the negative polarity clamp are summed together.   
     
     
       4. A symmetrical active clamp as recited in claim 3, wherein Vin is connected to the input terminal of the third amplifier.